Blood pump

ABSTRACT

A blood pump ( 1 ) comprises a pump casing ( 2 ) having a blood flow inlet ( 5 ) and a blood flow outlet ( 6 ) connected by a passage ( 7 ), and an impeller ( 3 ) arranged in said pump casing ( 2 ) so as to be rotatable about an axis of rotation ( 9 ). The impeller ( 3 ) is provided with blades ( 4 ) sized and shaped for conveying blood along the passage ( 7 ) from the blood flow inlet ( 5 ) to the blood flow outlet ( 6 ), the impeller ( 3 ) being rotatably supported in the pump casing ( 2 ) by at least one contact-type bearing ( 20 ) comprising a bearing surface of the impeller ( 3 ) facing a bearing surface of the pump casing ( 2 ). At least one wash out channel ( 30 ) extends through the impeller ( 3 ) and is in fluid connection with the passage ( 7 ) via a first opening ( 34 ) and with the bearing ( 20 ) via a second opening ( 35 ). The wash out channel ( 30 ) is operatively associated with a secondary pump for pumping blood through the wash out channel ( 30 ) towards the bearing ( 20 ), wherein the secondary pump is formed at least partially by said at least one wash out channel ( 30 ) extending through the impeller ( 3 ) along a direction having at least one tangential directional component.

BACKGROUND

This invention relates to blood pumps to be implanted in a patient forsupporting the patient's heart. In particular, the blood pump may beused as a “bridge to recovery” device, whereby the blood pumptemporarily supports the patient's heart until it has sufficientlyrecovered.

Blood pumps of different types are known, such as axial blood pumps,centrifugal blood pumps or mixed type blood pumps, where the blood flowis caused by both axial and radial forces. Blood pumps may be insertedinto a patient's vessel such as the aorta by means of a catheter, or maybe placed in the thoracic cavity. A blood pump typically comprises apump casing having a blood flow inlet and a blood flow outlet connectedby a passage. In order to cause a blood flow along the passage from theblood flow inlet to the blood flow outlet an impeller is rotatablysupported within the pump casing, with the impeller being provided withblades for conveying blood.

The impeller is supported within the pump casing by means of at leastone bearing, which may be of different types depending on the intendeduse of the blood pump, for instance whether the blood pump is intendedonly for short term use (some hours or some days) or long term use(weeks or years). A variety of bearings are known, such as contact-typebearings and non-contact bearings. In non-contact bearings the bearingsurfaces do not contact each other, e.g. in magnetic bearings, in whichthe bearing surface “levitate” due to repelling magnetic forces.Generally, contact-type bearings may include all types of bearings, inwhich the bearing surfaces may contact at least partially duringoperation of the pump at any time (i.e. always or intermittently), e.g.in slide bearings, pivot bearings, hydrodynamic bearings, hydrostaticbearings, ball bearings etc. or any combination thereof. In particular,contact-type bearings may be “blood immersed bearings”, where thebearing surfaces have blood contact. Contact-type bearings may heat upduring use and are subject to mechanical wear caused by the contact ofthe rotating bearing surface and the static bearing surface duringoperating of the pump. It is desirable to supply a cooling fluid to thebearing, such as the blood itself. In non-contact-type bearings, thebearing surfaces do not have physical contact but are spaced by aclearance, which is in fluid connection with the passage or other fluidsupply. Likewise, other clearances between the impeller and the pumpcasing should be washed out to avoid blood clotting and clogging, forinstance at the downstream front face of the impeller.

Arrangements for rinsing clearances or bearing surfaces within a bloodpump are disclosed for instance in US 2011/0238172 A1. Wash out channelsextend through the impeller and are in fluid communication with thepassage and the clearance via first and second openings. The pressuredistribution in the pump casing, where the pressure increases along theimpeller in a downstream direction, gives rise to a blood flow throughthe clearance and the wash out channel, the blood entering the clearanceat a downstream end of the impeller and flowing through the wash outchannel towards an area of the passage with lower pressure. This washout flow has the disadvantage of depending on the rotational speed ofthe impeller, because a pressure difference must be created to cause theblood flow. Other forces such as centrifugal forces and a counter forcedue to the backward direction of the wash out flow also have to beovercome. In another embodiment disclosed in US 2011/0238172 A1, inwhich the impeller is supported in the pump casing by a hydrodynamicbearing, the inlet opening of the wash out channel is disposed at theupstream end of the impeller. Secondary blades at the downstream end ofthe impeller are provided to cause a wash out flow through the wash outchannel and the clearance in a direction from an area of low pressure toan area of higher pressure.

SUMMARY OF THE INVENTION

It is therefore a primary object of the present invention to provide ablood pump wherein blood flow stagnation and blood clotting and cloggingin clearances between rotating parts and static parts of the blood pump,in particular between the static and rotating parts of the bearing orthe impeller and the pump casing, are effectively avoided, in particularindependently of the rotational speed or operating conditions of thepump. It is a further object of the present invention to provide a bloodpump that allows for effective cooling of a contact-type bearing. It isstill a further object of the present invention to provide a blood pumpwherein clearances can be effectively washed out.

The primary object is achieved according to the present invention by ablood pump with the features of independent claim 1. Preferredembodiments and further developments of the invention are specified inthe claims dependent thereon.

Like known blood pumps, the blood pump according to the inventioncomprises a pump casing having a blood flow inlet and a blood flowoutlet connected by a passage. The pump casing may be understood ascomprising all static parts of the blood pump. An impeller or rotor isarranged in said pump casing so as to be rotatable about an axis ofrotation, which may be the longitudinal axis of the impeller, whereinthe impeller is provided with blades sized and shaped for conveyingblood along the passage from the blood flow inlet to the blood flowoutlet. The impeller is rotatably supported in the pump casing by atleast one contact-type bearing, preferably a pivot bearing, comprising abearing surface of the impeller facing a bearing surface of the pumpcasing.

At least one wash out channel extends through the impeller and is influid connection with the passage via a first opening and with thebearing via a second opening. In order to cause a wash out flow, whichmay be denoted as active wash out flow, the wash out channel isoperatively associated with a secondary pump for pumping blood throughthe wash out channel towards the bearing. According to the invention,the secondary pump is formed at least partially by said at least onewash out channel which extends through the impeller along a directionhaving at least one tangential directional component. In other words,the second pump is particularly formed at least partially by said atleast one wash out channel itself which is sized, shaped and arranged soas to pump blood through the wash out channel towards the bearing. Byproviding a secondary pump that causes an active wash out flow, rinsingof the contact-type bearing and thereby cooling of the bearing can beimproved compared to an arrangement without means that actively pumpblood towards the bearing. The secondary pump may be supported by asuitable pressure distribution within the pump, which is described inmore detail below. It will be appreciated, however, that the secondarypump works independently of the pressure distribution within the pump.

The active wash out flow is particularly useful for cooling acontact-type bearing or a “blood immersed bearing”, since the amount ofblood that is delivered to the bearing to wash out and cool the bearingis increased compared to a pump without a secondary pump. Cooling of thebearing can be further improved by effectively dissipating the heat fromthe bearing surfaces. For this purpose, the bearing may comprise ahighly conductive material, such as stainless steel, that can dissipatethe heat better than e.g. ceramics or titanium. It may be advantageousto provide a bearing with at least two components, in particular wherethe bearing surface is made of a smooth and resistant material, such asceramics, e.g. provided in the form of a ceramic cap, while a portion ofthe bearing facing away from the bearing surface may be made of a highlyconductive material, such as stainless steel.

In one embodiment, the wash out channel may extend linearly through theimpeller and be offset relative to the axis of rotation. In particular,the wash out channel may extend in a plane that is parallel to the axisof rotation. By providing an arrangement having linear wash out channelsthat are skew with respect to the axis of rotation, i.e. do notintersect the axis of rotation, it is possible to cause an active washout flow through the wash out channel.

In another embodiment, the wash out channel may be curved and extendfrom the first opening in a direction around the axis of rotation, inparticular along a spiral shape. A spiral shape is to be understood asany curved, spiral, helical or otherwise curved shape in a directionabout the axis of rotation at any length. Such shape is advantageousbecause it may support an active wash out flow towards the bearing.

Preferably, the wash out channel extends from the first opening at anangle relative to a surface of the impeller in a circumferentialdirection opposite the direction of rotation. In particular in contrastto a wash channel that extends perpendicularly to the surface of theimpeller, an angled inlet opening facilitates the entrance of blood intothe wash out channel and increases the flow rate through the wash outchannel. This effect may be further improved by choosing an appropriateangle. For instance, the angle may be less than 20°, preferably lessthan 15°, more preferably less than 10°. The wash out channel may extendfrom the first opening in a substantially tangential direction relativeto a surface of the impeller, in other words at a very small angle withrespect to the surface of the impeller. It is important, however, thatthe angle is in a circumferential direction opposite the direction ofrotation, in other words that the first opening opens in the directionof rotation to increase the amount of blood that flows through the washout channel compared to an arrangement in which the wash out channelextends perpendicularly to the surface of the impeller.

In an embodiment, a distance between the second opening and the axis ofrotation may be less than or equal to a distance between the firstopening and the axis of rotation. In other words, in a downstreamdirection, the wash out channel extends in a direction towards the axisof rotation. Preferably, in order to reduce the centrifugal forces thathave to be overcome by the wash out flow within the wash out channel, adistance between the first opening and the axis of rotation is as smallas possible. In other words, the distance between the first opening andthe second opening in a radial inward direction should be as small aspossible. It is further preferable if the distance between the axis ofrotation and the first opening is significantly smaller than a distancebetween the axis of rotation and a point where the wash out flow exitsto the passage, e.g. half (50%) or less than half, less than 40% or evenless than 30%. This arrangement can be improved, i.e. the distancebetween the first opening and the point where the wash out flow exits tothe passage can be increased, in centrifugal blood pumps compared toaxial or mixed-type blood pump.

The impeller may comprise a central opening extending along the axis ofrotation and accommodating the bearing, wherein the second opening is influid connection with the central opening. Furthermore, the wash outchannel may be directed towards the axis of rotation substantially in aradial direction at the second opening. This may improve rinsing of thebearing and thereby cooling of the bearing.

Preferably, the first opening of the wash out channel is disposedadjacent to one of the blades of the impeller on a forward side of theblade with respect to the direction of rotation (generally referred toas the positive pressure side of the blade). In this area, the pressureis higher in particular compared to an area on a backward side of theblade (generally referred to as the negative pressure side of theblade), such that an active wash out flow through the wash out channeltowards the bearing can be improved. In an embodiment, the first openingmay be disposed on the forward side of the blade, while the secondopening may be disposed on the backward side of the blade, that is tosay both openings are disposed on a radially outer surface of theimpeller and the wash out channel extends underneath and crosses theblade. In another embodiment, the wash out channel may extend within theblade, whereby the first opening is disposed on the forward side of theblade and the second opening is disposed in the blade, in particular ona radially outer edge of the blade. It is to be understood that the washout channel is in fluid communication with the areas to be washed out.

As explained, the performance or output of the secondary pump can beimproved by a specific arrangement of the wash out channel through theimpeller, for instance a linear or curved wash out channel, which mayextend at an angle relative to the surface of the impeller. Theperformance of the secondary pump may be further improved by the crosssection of the first opening of the wash out channel. The cross sectionof the first opening may be circular or non-circular. In case the washout channel has a circular cross section and extends at an anglerelative to the surface of the impeller, this will result in anon-circular cross-section, such as an elliptical cross-section. In anembodiment, the first opening may be formed by an end portion of thewash out channel that is at least partially exposed due to an incline ofthe wash out channel relative to a surface of the impeller. In otherwords, the first opening may be elongate on the surface of the impeller,which may further increase the amount of blood that enters the wash outchannel during operation of the blood pump.

In another embodiment, a protrusion may extend into the first opening ofthe wash out channel, being sized and shaped to increase a blood flowthrough the first opening into the wash out channel, in particularcompared to a cross section of the first opening without the protrusion.The shape of the first opening without the protrusion may be eithercircular or non-circular. The protrusion may be disposed on a backwardside of the first opening relative to the direction of rotation suchthat it acts as an “airfoil” to promote inflow of blood into the firstopening and thereby improve performance of the secondary pump.Alternatively or additionally, the impeller may comprise a wingextending radially therefrom and being disposed adjacent to and behindthe first opening of the wash out channel with respect to the directionof rotation. Preferably, the wing extends over the first opening of thewash out channel and opens in the direction of rotation so as to allowblood to enter the first opening. The wing forms a pocket that collectsblood during rotation of the impeller and directs the collected bloodinto the first opening. In order to achieve a similar effect, theimpeller may comprise a nose or protrusion comprising the first openingsuch that the cross section of the first opening extends at an anglerelative to the surface of the impeller, preferably an angle greaterthan 45°, more preferably an angle of 90°, and opens in the direction ofrotation. This may significantly increase the amount of blood that flowsinto the wash out channel.

Preferably, the blood pump comprises two or more of the above describedwash out channels that may be symmetrically arranged with respect to theaxis of rotation. In particular, the blood pump may comprise two, three,four, five or six wash out channels.

In addition to the size, shape and arrangement of the wash out channelsforming at least part of the secondary pump, the secondary pump mayfurther comprise grooves or blades formed in a surface of the impeller.Such secondary grooves or blades may be disposed at a downstream frontface of the impeller to support the blood flow through the wash outchannel towards the bearing.

In an embodiment, the impeller may have a portion in a downstreamdirection extending radially outward, the first opening of the wash outchannel being disposed in said portion. In particular, said portionconically tapers radially outward in a downstream direction. The portionmay be integrally formed with the impeller or separately formed. Theperformance of the secondary pump may be further increased by arrangingthe first opening in a radially extending portion of the impeller suchthat it is directed in a direction opposite the main direction of theblood flow through the passage. The first opening may then catch moreblood and improve the performance of the secondary pump. The blades ofthe impeller may extend over said portion.

In a preferred embodiment, the first opening of the wash out channel isarranged in an area of the impeller that—during operation of the pump—isunder a higher pressure than the second opening so as to cause a bloodflow from the first opening through the wash out channel to the bearing.In other words, the wash out flow is directed in a “forward” direction,that is to say, in a direction towards the blood flow outlet of the pumpcasing, because the first opening of the wash out channel, i.e. an inletopening of the wash out channel, is in a high pressure area of theimpeller, while at the downstream side of the impeller the pressure islower. Thus, by utilizing this pressure difference, in particular thelocal pressure gradient within the wash out channel, that occurs duringoperation of the blood pump, a forward flow wash out is created. Thishas the advantage that the necessary pressure difference is present atany time during operation of the pump, independent of the rotationalspeed and operating condition (e.g. preload, afterload, magnitude ofprimary forward flow), in particular also at a beginning of operation,when the rotation of the impeller starts and the rotational speed islow, in particular below the design speed of the blood pump. Incontrast, in known blood pumps, where the wash out flow is directed in a“backward” direction, a pressure difference has to be built up, whichtakes some time during which the wash out flow is slow or may stagnate.This may lead to blood clotting and clogging in the clearance or thewash out channel or both. Furthermore, a backward flow has to overcomeforces caused by the main direction of flow, which may also lead tostagnation of the wash out flow and consequently blood clotting andclogging. According to the present invention, a wash out flow in a“forward” direction is present throughout the time of operation of theblood pump, in particular utilizing the pressure distribution within thepump casing during operation of the pump.

The first opening of the wash out channel may be disposed in adownstream half of the impeller. During operation of the pump, thepressure increases along the length of the impeller, in particular in aregion where the blades of the impeller are disposed. Therefore, in thedownstream half of the impeller, a higher pressure is present than inthe upstream half of the impeller. Since a high pressure at the firstopening of the wash out channel is preferred, it is preferable to placethe first opening in the downstream half of the impeller. Morepreferably, the first opening may be placed in a downstream third, adownstream quarter or a downstream fifth of the impeller. In particular,it is advantageous to place the first opening as close as possible tothe downstream end of the impeller, for instance within the last 10percent of the length of the impeller in the downstream direction.

In terms of the pressure distribution, the first opening of the wash outchannel preferably is disposed in an area of the impeller where—duringoperation of the pump—the pressure is higher than a median pressure withrespect to a pressure distribution along a length of the passage wherethe impeller is situated, more preferably where the pressure issubstantially the maximum pressure. A high pressure difference betweenthe first and second openings of the wash out channel improves the washout flow from the first opening of the wash out channel to the bearing.In particular, a high pressure difference is advantageous to support thesecondary pump.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments, will be better understood when read inconjunction with the appended drawings. For the purpose of illustratingthe present disclosure, reference is made to the drawings. The scope ofthe disclosure is not limited, however, to the specific embodimentsdisclosed in the drawings. In the drawings:

FIG. 1 shows a cross sectional view of a blood pump according to theinvention for extracardiac use.

FIG. 2 shows a cross sectional view of a blood pump according to theinvention designed as a catheter pump.

FIG. 3 shows a perspective view of an impeller.

FIGS. 4a to 4d show different views of a portion of an impeller.

FIGS. 5a and 5b show other embodiments of an impeller.

FIGS. 6a and 6b show other embodiments of a portion of an impeller.

FIG. 7 shows a cross sectional view of a part of a blood pump accordingto another embodiment.

FIG. 8 shows a cross sectional view of a part of an impeller accordingto another embodiment.

FIG. 9 shows a cross sectional view of a part of an impeller accordingto another embodiment.

FIG. 10 shows a cross sectional view of a part of an impeller accordingto still another embodiment.

FIG. 11 shows a cross sectional view of a part of a blood pump accordingto another embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, a cross sectional view of a blood pump 1 isillustrated. The blood pump 1 is designed for extracorporeal,extracardiac or extraluminal use and comprises a pump casing 2 with ablood flow inlet 5 and a blood flow outlet 6. During operation, the pumpcasing 2 is placed outside a patient's body and the blood flow inlet 5and the blood flow outlet 6 are connected to respective connectors (inparticular inflow from the heart and outflow to the aorta). FIG. 2 showsan embodiment that is similar to that of FIG. 1 with the difference thatit is designed as a catheter pump 1′. The blood flow inlet 5′ is at theend of a flexible cannula 50 which is placed through a heart valve, suchas the aortic valve, during use, while the blood flow outlet 6′ isplaced in a side of the pump casing 2′ and is placed in a heart vessel,such as the aorta. The blood pump 1′ is connected to a catheter 51, andan electric wire 52 extends through the catheter 51 for driving the pump1′. Both blood pumps 1 and 1′ function in the same way. It will beappreciated that all features described below are applicable for bothembodiments.

The blood is conveyed along a passage 7 connecting the blood flow inlet5 and the blood flow outlet 6. An impeller 3 is provided for conveyingblood along the passage 7 and is rotatably mounted about an axis ofrotation 9 within the pump casing 2 by means of a first bearing 10 and asecond bearing 20. The axis of rotation is preferably the longitudinalaxis of the impeller 3. Both bearings 10, 20 are contact-type bearings.At least one of the bearings 10, 20, however, could be anon-contact-type bearing, such as a magnetic or hydrodynamic bearing.The second bearing 20 is a pivot bearing having spherical bearingsurfaces that allow for rotational movement as well as pivoting movementto some degree. The first bearing 10 is disposed in a supporting member15 to stabilize the rotation of the impeller 3, the supporting member 15having at least one opening 16 for the blood flow. Blades 4 are providedon the impeller 3 for conveying blood once the impeller 3 rotates.Rotation of the impeller 3 is caused by an electric motor stator 8magnetically coupled to an end portion 37 of the impeller 3. Othersuitable driving mechanisms are possible as will be appreciated by aperson skilled in the art. The illustrated blood pump 1 is a mixed-typeblood pump, wherein the major direction of flow is axial. It will beappreciated that the blood pump 1 could also be a purely axial bloodpump, depending on the arrangement of the impeller 3, in particular theblades 4.

The impeller 3 comprises a portion 33 that is disposed in a downstreamportion of the impeller 3 and extends radially outwards. The portion 33can be denoted as a yoke, flange portion or end portion. In thisembodiment, the portion 33 comprises an outer surface that extends at anangle of 45° with respect to the axis of rotation 9. Other appropriateangles could be chosen, e.g. an angle between 30° and 60° or could be acurved surface. The portion 33 may be formed integrally with theimpeller 3 or separately as shown in this embodiment. At least one washout channel 30, preferably two or more, such as three, four, five or sixwash out channels 30, only one of which is shown in FIG. 1, extendsthrough the impeller 3, in particular through the portion 33, so as toallow for washing out or rinsing the pivot bearing 20 and the clearance31 between the impeller 3 and a static part of the blood pump 1, inparticular the pump casing 2 or the motor 8, which may be regarded asassociated with the pump casing 2. The at least one wash out channel 30may also extend at least partially into the main portion of the impeller3 beyond the portion 33.

The wash out channel 30 has a first opening 34 or inlet opening and asecond opening 35 or outlet opening. The first opening 34 forms a fluidconnection between the passage 7 and the wash out channel 30, while thesecond opening 35 is in fluid connection with the clearance 31. Inparticular, the second opening 35 is in fluid connection with a centralbore or central opening 32 of the portion 33 accommodating the secondbearing 20. The clearance 31 is in fluid connection with the passage 7via a clearance transition point 36, i.e. a location where the clearance31 opens to the passage 7.

The first opening 34 of the wash out channel 30 is disposed in adownstream half of the impeller 3. In particular, the first opening 34is disposed in an area of the impeller 3 that is under a high pressurecaused by the rotation of the impeller 3 during operation of the bloodpump 1. In particular, the first opening 34 may be in an area close toor at the maximum pressure within the pump casing 2. The pressure isincreased by the blades 4 and by the deflection of fluid from an axialflow direction to a radial direction and then decreases downstream ofthe blades 4. Therefore, a pressure at the clearance transition point 36is lower than at the first opening 34 of the wash out channel 30 due toan appropriate choice of the position of the first opening 34, which isnear the downstream end of the impeller 3. This pressure distribution,which may be enhanced by choosing the shape of the blades 4 accordingly,results in a flow direction from the first opening 34 through the washout channel 30 and the clearance 31 to the clearance transition point36. Alternatively, a further drop in pressure at point 36 could beachieved by creating a local pressure drop by the Venturi effect in theproximity of point 36, e.g. by providing a narrowing 53 of the passage 7(see FIG. 1A). In other words, blood flows through the wash out channel30 in a forward direction towards the blood flow outlet 6 of the pumpcasing 2. Blood clotting can be effectively avoided at any time duringoperation of the blood pump 1, in particular also during phases with lowrotational speed below the design speed of the blood pump 1, because theforward flow wash out occurs at any rotational speed.

Apart from washing out the pivot bearing 20 and the clearance 31, theblood flow through the wash out channel 30 provides cooling for thepivot bearing 20. The pivot bearing 20 is arranged in the centralopening 32 of the portion 33. Thus, blood is conveyed through the washout channel 30 towards the bearing 20. The pivot bearing 20 can beeffectively cooled and rinsed. The effect can be further improved byproviding a secondary pump that actively pumps blood through the washout channel 30 towards the bearing 20 as will be described in detailbelow. Although a “forward” direction of the wash out flow through thewash out channels 30 as described is advantageous, the wash out flow maybe directed in any direction.

Now referring to FIG. 3, an embodiment of an impeller 3 is shown. Theimpeller has blades 4 arranged around a body of the impeller 3 and sizedand shaped for conveying blood when the impeller 3 rotates in adirection of rotation (indicated by an arrow in FIG. 3). The impeller 3has a portion 33 at its downstream end, wherein the portion 33 has atleast one wash out channel 30 having an inlet opening 34. As explainedabove, the inlet opening 34 is arranged in an area of the impeller 3that is under a high pressure to ensure that the blood flow through thewash out channel 30 is directed from the first opening 34 or inletopening to the second opening 35. In this embodiment, the inlet opening34 is disposed on a forward side of one of the blades 4 with respect tothe direction of rotation (also referred to as the positive pressureside of the blade). In particular compared to a backward side of theblade 4 (also referred to as the negative pressure side of the blade),the pressure is higher on the forward side, which supports the directionof flow into the inlet opening 34 of the wash out channel 30.Nevertheless, the opening 34 may be disposed on the backward side of theblade 4, where the pressure may be sufficiently high because the opening34 is disposed in the portion 33 at the downstream end of the impeller3.

In FIGS. 4a-4d different views of an embodiment of the portion 33 areshown. In this embodiment, the wash out channels 30 form a secondarypump that pumps the blood through the wash out channels 30 from therespective first opening 34 to the second opening 35 and, thus, to thecentral opening 32 and the bearing 20 and further to the clearancetransition point 36 (see FIG. 1). In this embodiment, the wash outchannels 30 extend linearly through the impeller 3 and are offset withrespect to the axis of rotation 9 (indicated by dashed lines in FIG. 4b, which is a bottom view of the portion 33). The wash out channels 30extend in planes that are parallel to the axis of rotation 9, such thatthe wash out channels 30 extend along a direction that has a tangentialcomponent. This arrangement enforces the blood flow in the directionfrom the first opening 34 towards the second opening 35. Two wash outchannels 30 are shown in this embodiment. It will be appreciated,however, that three, four or more wash out channel can likewise beprovided, which may be symmetrically arranged around the axis ofrotation 9. As can be seen particularly in FIG. 4d , which is a crosssectional view along line B-B in FIG. 4b , the wash out channels 30 areinclined in the downstream direction. The second openings 35, which aredownstream relative to the first openings 34, are closer to the axis ofrotation 9 than the first openings 34. The wash out channels 30 open tothe central opening 32 which at least partially accommodates the secondbearing 20 as shown in FIG. 1.

Further embodiments of an impeller 3 having wash out channels 30 thatform a secondary pump are shown in FIGS. 5a and 5b . According to theembodiment of FIG. 5a , the first opening 34 is not circular. Moreprecisely, a protrusion 38 extends into the first opening 34 forenhancing the amount of blood that flows through the first opening 34into the wash out channel. The protrusion 38 is arranged at a backwardside of the first opening 34 with respect to the direction of rotation.The resulting shape of the first opening 34 may be denoted as a kidneyshape. It acts like an “airfoil” such that a pull or suction is createdupon rotation of the impeller 3 to increase the amount of blood thatenters the first opening 34, in particular compared to an embodimentwithout the protrusion 38 (such as the embodiment of FIG. 3). The shapeof the protrusion 38 can be chosen according to the desired amount ofblood that should flow through the wash out channels 30. The crosssection of the first opening 34 may be symmetric or asymmetric.

Alternatively or in addition to the protrusion 38, a wing 39 can beprovided as shown in FIG. 5b . The wing 39 is arranged behind the firstopening 34 with respect to the direction of rotation and forms a pocketto catch a larger amount of blood upon rotation of the impeller 3 in thedirection of rotation. The wing 39 may have any size and shape that issuitable to increase the amount of blood that enters the first opening34 compared to an embodiment without the wing 39 (such as the embodimentof FIG. 3). The same effect can be achieved by arranging the firstopening 34 in a nose or protrusion that extends radially from theimpeller 3, with the first opening 34 pointing in the direction ofrotation.

Referring now to FIGS. 6a and 6b , an embodiment of a portion 33′ havingwash out channels 30′ is shown. The direction of rotation is indicatedby an arrow. As in the above described embodiments, the wash outchannels 30′ have a first opening 34′ and a second opening 35′ facing acentral opening 32′. The wash out channels 30′ form part of a secondarypump as described in connection with the other embodiment to force ablood flow in a direction from the first openings 34′ to the secondopenings 35′ towards the second bearing 20. In this embodiment, the washout channels 30′ are curved and extend around the axis of rotation 9 ina spiral shape. It will be appreciated that the term “spiral shape”comprises any curved shape, whether it forms a regular spiral or anyother curved shape having at least one tangential component. The washout channels 30′ enter the impeller 3 at the first opening at a smallangle such that the first opening 34′ is formed by an exposed portion ofthe wash out channel 30′ and has an elongate shape. This promotescatching blood and helps to increase the amount of blood that enters thefirst opening 34′, in particular compared to an arrangement in which thewash out channels 30 extend to the surface of the impeller 3 at a largeangle, such as perpendicular or substantially perpendicular. The washout channels 30′ extend in a curved shape towards the central opening32′ and exit at the second openings 35′ in a substantially radialdirection. Blood is effectively pumped into the central opening 32′ andthus to the second bearing 20, such that the second bearing 20 is rinsedand cooled. As explained in connection with FIG. 1, the blood flowthrough the wash out channels 30′ effectively washes out the clearance31 between the rotating impeller 3 and the static pump casing 2. Inorder to further improve the performance of the secondary pump, thesecondary pump may further comprise grooves or blades formed on asurface of the impeller 3, in particular in the clearance 31.

It shall be understood that the secondary pump described above cannotovercome the centrifugal effect of a rotating channel of any shape thatextends from a larger diameter to a smaller diameter without theassistance of the centrifugal pumping action at clearance 31.

The performance of the secondary pump may be further improved by theposition of at least one of the first opening 34 and the clearancetransition point 36 relative to the rotational axis 9 and in particularrelative to each other. As shown in FIG. 7 the first opening has a firstdistance d₁ to the rotational axis 9, while the clearance transitionpoint 36 has a second distance d₂ to the rotational axis 9. Theperformance of the secondary pump can be improved if the first opening34 is as close as possible to the rotational axis, that is to say if thedistance d₁ is as small as possible and the wash out channel 30 extendsonly a little distance towards the rotational axis 9. This reducescentrifugal forces that have to be overcome by the wash out flow flowingin a direction towards the rotational axis. In particular, it isadvantageous if the first distance d₁ is small compared to the seconddistance d₂, preferably d₁ may be half of d₂ or less.

In another embodiment, shown in the cross section perpendicular to therotational axis 9 in

FIG. 8, the impeller 3 includes a wash out channel 40 with the firstopening 41 and the second opening 42 being disposed on a radiallyoutward surface of the impeller 3. The first opening 41 is disposed on aforward side of one of the blade 4 with respect to the direction ofrotation (indicated by an arrow in FIG. 8), while the second opening 42is disposed on a backward side of the blade 4. This causes a blood flowfrom the first opening 41 to the second opening 42. The wash out channel40 is in fluid communication with the central opening 32 to wash out andcool the bearing 20. In the embodiment of FIG. 9, a wash out channel 43is provided that has a first opening 44 disposed on a forward side ofone of the blades 4 similar to the embodiment of FIG. 8. However, thewash out channel 43 extends through the blade 4 and exits at the secondopening 45 which is arranged at an edge of the blade 4. This arrangementallows utilizing centrifugal forces to enforce a wash out flow from thefirst opening 44 to the second opening 45. FIG. 10 depicts anotherembodiment similar to that of FIG. 9. However, the first opening 44′ ofthe wash out channel 43′ is disposed diagonally opposite to the blade 4through which the channel 43′ extends and where the channel 43′ exits atthe second opening 45′. Thus, in this embodiment the wash out channel43′ runs diagonally or radially rather than tangential as in theembodiment of FIG. 9, such that it touches all sides of the bearing 20.

An embodiment similar to that of FIG. 8 is shown in FIG. 11. The washout channel 40′ has a first opening 41′ disposed on a forward side ofone of the blade 4 with respect to the direction of rotation, while thesecond opening 42′ is disposed on a backward side of the blade 4 (pleasenote that the wash out channel 40′ is shown in the cross-sectional viewof FIG. 11 although it does not extend in the plane of the cross sectionbut rather similar to the cross-section shown in FIG. 8). The wash outchannel 40′ extends underneath the blade 4. However, in the embodimentof FIG. 11 the wash out channel 40′ does not extend in one plane that isperpendicular to the longitudinal axis 9, but the second opening 42′ isdisposed downstream of the first opening 41′. Thus, the second opening42′ is also disposed radially outwards from the first opening 41′. Thewash out flow can be increased by this arrangement by centrifugal forcesin the exit section of the wash out channel 40′ leading to the secondopening 42′. Also the pressure difference in the passage 7 between thefirst opening 41′ and second opening 42′ enhances the wash out flow.

It will be appreciated that at least one of the wash out channels 40,40′, 43, 43′ described in connection with FIGS. 8 to 11 may be providedalternatively or in addition to the aforementioned wash out channels 30,30′. Also to be understood, channels 40, 40′, 43, 43′ are in fluidcommunication with the central opening 32 and the clearance 31, thusallowing for a net washout flow in the same manner described above.

Preferred embodiments are described in the following paragraphs:

1. A blood pump 1, comprising:

a pump casing 2 having a blood flow inlet 5 and a blood flow outlet 6connected by a passage 7,

an impeller 3 arranged in said pump casing 2 so as to be rotatable aboutan axis of rotation 9, the impeller 3 being provided with blades 4 sizedand shaped for conveying blood along the passage 7 from the blood flowinlet 5 to the blood flow outlet 6, the impeller 3 being rotatablysupported in the pump casing 2 by at least one contact-type bearing 20comprising a bearing surface of the impeller 3 facing a bearing surfaceof the pump casing 2,

wherein at least one wash out channel 30 extends through the impeller 3and is in fluid connection with the passage 7 via a first opening 34 andwith the bearing 20 via a second opening 35, the wash out channel 30being operatively associated with a secondary pump for pumping bloodthrough the wash out channel 30 towards the bearing 20,

wherein the secondary pump is formed at least partially by said at leastone wash out channel 30 extending through the impeller 3 along adirection having at least one tangential directional component.

2. The blood pump of paragraph 1, wherein the wash out channel 30extends linearly through the impeller 3 and is offset relative to theaxis of rotation 9.

3. The blood pump of paragraph 2, wherein the wash out channel 30extends in a plane that is parallel to the axis of rotation 9.

4. The blood pump of paragraph 1, wherein the wash out channel 30 iscurved and extends from the first opening 34 in a direction around theaxis of rotation 9.

5. The blood pump of any one of paragraphs 1 to 4, wherein the wash outchannel 30 extends from the first opening 34 at an angle relative to asurface of the impeller 3 in a circumferential direction opposite thedirection of rotation.

6. The blood pump of paragraph 5, wherein the angle is less than 20°,preferably less than 15°, more preferably less than 10°.

7. The blood pump of paragraph 5 or 6, wherein the wash out channel 30extends from the first opening 34 in a substantially tangentialdirection relative to a surface of the impeller 3.

8. The blood pump of any one of paragraphs 1 to 7, wherein a distancebetween the second opening 35 and the axis of rotation 9 is less than orequal to a distance between the first opening 34 and the axis ofrotation 9.

9. The blood pump of any one of paragraphs 1 to 8, wherein a distancebetween the axis of rotation 9 and the first opening 34 is less than50%, preferably less than 40%, more preferably less than 30% of adistance between the axis of rotation 9 and a point 36 where the washout flow exits to the passage 7.

10. The blood pump of any one of paragraphs 1 to 9, wherein the impeller3 comprises a central opening 32 extending along the axis of rotation 9and accommodating the bearing 20, wherein the second opening 35 is influid connection with the central opening 32.

11. The blood pump of any one of paragraphs 1 to 10, wherein the washout channel 30 at the second opening 35 is directed towards the axis ofrotation 9 substantially in a radial direction.

12. The blood pump of any one of paragraphs 1 to 11, wherein the firstopening 34 of the wash out channel 30 is disposed adjacent to one of theblades 4 of the impeller 3 on a forward side of the blade 4 with respectto the direction of rotation.

13. The blood pump of any one of paragraphs 1 to 12, wherein a crosssection of the first opening 34 is circular.

14. The blood pump of any one of paragraphs 1 to 12, wherein a crosssection of the first opening 34 is non-circular.

15. The blood pump of any one of paragraphs 1 to 13, wherein the firstopening 34 is formed by an end portion of the wash out channel 30 thatis at least partially exposed due to an incline of the wash out channel30 relative to a surface of the impeller 3.

16. The blood pump of any one of paragraphs 1 to 15, wherein aprotrusion 38 extends into the first opening 34 of the wash out channel30 and is sized and shaped to increase a blood flow through the firstopening 34 into the wash out channel 30.

17. The blood pump of any one of paragraphs 1 to 16, wherein theimpeller 3 comprises at least one wing 39 extending radially therefromand being disposed adjacent to and behind the first opening 34 of thewash out channel 30 with respect to the direction of rotation.

18. The blood pump of paragraph 17, wherein the wing 39 extends over thefirst opening 34 of the wash out channel 30 and opens in the directionof rotation so as to allow blood to enter the first opening 34.

19. The blood pump of any one of paragraphs 1 to 16, wherein theimpeller 3 comprises a protrusion extending radially therefrom, theprotrusion comprising the first opening 34 such that a cross section ofthe first opening 34 extends at an angle relative to the surface of theimpeller 3 and opens in the direction of rotation, wherein the anglepreferably is greater than 45°, more preferably 90°.

20. The blood pump of any one of paragraphs 1 to 19, comprising two ormore wash out channels 30 that are symmetrically arranged with respectto the axis of rotation 9.

21. The blood pump of any one of paragraphs 1 to 20, wherein thesecondary pump comprises grooves or blades formed in a surface of theimpeller 3.

22. The blood pump of any one of paragraphs 1 to 21, wherein theimpeller 3 has a portion 33 in a downstream direction extending radiallyoutward, the first opening 34 of the wash out channel 30 being disposedin said portion 33.

23. The blood pump of paragraph 22, wherein said portion 33 conicallytapers radially outward in a downstream direction.

24. The blood pump of paragraph 22 or 23, wherein the blades 4 of theimpeller 3 extend over said portion 33.

25. The blood pump of any one of paragraphs 22 to 24, wherein theportion 33 is integrally formed with the impeller 3 or separatelyformed.

26. The blood pump of any one of paragraphs 1 to 25, wherein the firstopening 34 of the wash out channel 30 is disposed in a downstream halfof the impeller 3.

27. The blood pump of any one of paragraphs 1 to 26, wherein the firstopening 34 of the wash out channel 30 is disposed in an area of theimpeller 3 that—during operation of the blood pump 1—is under a higherpressure than an area of the impeller 3 where the bearing 20 is disposedso as to cause a blood flow from the first opening 34 through the washout channel 30 to the bearing 20.

28. The blood pump of any one of paragraphs 1 to 27, wherein the bloodflow from the first opening 34 through the wash out channel 30 is in adirection towards the blood flow outlet 6 of the pump casing 2.

29. The blood pump of any one of paragraphs 1 to 28, wherein the firstopening 41 is disposed on a forward side of the blade 4, and the secondopening 42 is disposed on a backward side of the blade 4, and the washout channel 40 extends underneath the blade 4.

30. The blood pump of any one of paragraphs 1 to 29, wherein the washout channel 43 extends within the blade 4, wherein the first opening 44is disposed on a forward side of the blade 4 and the second opening 45is disposed in the blade 4, preferably on a radially outer edge of theblade 4.

31. The blood pump of any one of paragraphs 1 to 30, wherein thecontact-type bearing 20 is a pivot bearing.

32. The blood pump of any one of paragraphs 1 to 31, wherein the bloodpump 1 is an axial blood pump, a centrifugal blood pump or a mixed-typeblood pump.

1. A blood pump (1), comprising: a pump casing (2) having a blood flowinlet (5) and a blood flow outlet (6) connected by a passage (7), animpeller (3) arranged in said pump casing (2) so as to be rotatableabout an axis of rotation (9), the impeller (3) being provided withblades (4) sized and shaped for conveying blood along the passage (7)from the blood flow inlet (5) to the blood flow outlet (6), the impeller(3) being rotatably supported in the pump casing (2) by at least onecontact-type bearing (20) comprising a bearing surface of the impeller(3) facing a bearing surface of the pump casing (2), wherein at leastone wash out channel (30) extends through the impeller (3) and is influid connection with the passage (7) via a first opening (34) and withthe bearing (20) via a second opening (35), the wash out channel (30)being operatively associated with a secondary pump for pumping bloodthrough the wash out channel (30) towards the bearing (20), wherein thesecondary pump is formed at least partially by said at least one washout channel (30) extending through the impeller (3) along a directionhaving at least one tangential directional component.
 2. The blood pumpof claim 1, wherein the wash out channel (30) extends linearly throughthe impeller (3) and is offset relative to the axis of rotation (9),wherein the wash out channel (30) preferably extends in a plane that isparallel to the axis of rotation (9).
 3. The blood pump of claim 1,wherein the wash out channel (30) is curved and extends from the firstopening (34) in a direction around the axis of rotation (9).
 4. Theblood pump of any one of claims 1 to 3, wherein the wash out channel(30) extends from the first opening (34) at an angle relative to asurface of the impeller (3) in a circumferential direction opposite thedirection of rotation, wherein the angle preferably is less than 20°,preferably less than 15°, more preferably less than 10°.
 5. The bloodpump of any one of claims 1 to 4, wherein a distance between the axis ofrotation (9) and the first opening (34) is less than 50%, preferablyless than 40%, more preferably less than 30% of a distance between theaxis of rotation (9) and a point (36) where the wash out flow exits tothe passage (7).
 6. The blood pump of any one of claims 1 to 5, whereinthe impeller (3) comprises a central opening (32) extending along theaxis of rotation (9) and accommodating the bearing (20), wherein thesecond opening (35) is in fluid connection with the central opening(32), wherein preferably the wash out channel (30) at the second opening(35) is directed towards the axis of rotation (9) substantially in aradial direction.
 7. The blood pump of any one of claims 1 to 6, whereinthe first opening (34) of the wash out channel (30) is disposed adjacentto one of the blades (4) of the impeller (3) on a forward side of theblade (4) with respect to the direction of rotation.
 8. The blood pumpof any one of claims 1 to 7, wherein a cross section of the firstopening (34) is circular or non-circular.
 9. The blood pump of any oneof claims 1 to 8, wherein the first opening (34) is formed by an endportion of the wash out channel (30) that is at least partially exposeddue to an incline of the wash out channel (30) relative to a surface ofthe impeller (3).
 10. The blood pump of any one of claims 1 to 9,wherein a protrusion (38) extends into the first opening (34) of thewash out channel (30) and is sized and shaped to increase a blood flowthrough the first opening (34) into the wash out channel (30), and/orwherein the impeller (3) comprises at least one wing (39) extendingradially therefrom and being disposed adjacent to and behind the firstopening (34) of the wash out channel (30) with respect to the directionof rotation, wherein the wing (39) preferably extends over the firstopening (34) of the wash out channel (30) and opens in the direction ofrotation so as to allow blood to enter the first opening (34).
 11. Theblood pump of any one of claims 1 to 10, comprising two or more wash outchannels (30) that are symmetrically arranged with respect to the axisof rotation (9).
 12. The blood pump of any one of claims 1 to 11,wherein the impeller (3) has a portion (33) in a downstream directionextending radially outward, the first opening (34) of the wash outchannel (30) being disposed in said portion (33).
 13. The blood pump ofany one of claims 1 to 12, wherein the first opening (34) of the washout channel (30) is disposed in a downstream half of the impeller (3).14. The blood pump of any one of claims 1 to 13, wherein the firstopening (34) of the wash out channel (30) is disposed in an area of theimpeller (3) that—during operation of the blood pump (1)—is under ahigher pressure than an area of the impeller (3) where the bearing (20)is disposed so as to cause a blood flow from the first opening (34)through the wash out channel (30) to the bearing (20).
 15. The bloodpump of any one of claims 1 to 14, wherein the blood flow from the firstopening (34) through the wash out channel (30) is in a direction towardsthe blood flow outlet (6) of the pump casing (2).